This application relies for priority upon Korean Patent Application No. 2000-17986, filed on Apr. 6, 2000, the contents of which are herein incorporated by reference in their entirety.
This invention relates to a photolithography system and process for manufacturing a semiconductor device. More particularly, this invention relates to a system for adjusting a photo-exposure time suitable for variable processing conditions in accordance with prior and following steps.
The greater a semiconductor device is integrated, the more line widths on the device must be narrowed. Furthermore, as the line width is reduced, more accurate alignment is required for patterns of stacked layers formed through a manufacturing process for the semiconductor device. Of all of the various pieces of equipment required for manufacturing semiconductor devices, a photo-exposure apparatus is the most important for determining the alignment accuracy for the stacked layers. In other words, in modem semiconductor manufacturing, a photo-exposure apparatus must have improved capacities for high resolution and fine alignment so as to be capable of manufacturing highly-integrated semiconductor devices.
Various techniques have been used for highly efficient photo-exposure apparatuses. For example, in order to enhance the alignment accuracy in semiconductor device manufacturing technology and to uniformly obtain a fine pattern in an accurate position, conventional G-Line light sources, with a wavelength of 436 nm, are gradually being replaced by I-Line light sources, with a wavelength of 365 nm, or deep ultra violet light sources, with a wavelength of 248 nm. Furthermore, a scanner-type source is dominantly being used rather than a stepper-type source.
There are several factors, such as a kind of lens system used or the light source used that influence the accuracy of a photo-exposure apparatus. In addition, an exposure time adjusting method, the kind and thickness of a photoresist material used, the baking conditions, the developing conditions, etc. may also effect the resultant quality of a photo-exposure work. In particular, a photo-exposure time is a very important parameter to finalize a line width and a uniformity of the pattern geometry. This is because photo-exposure time has an effect at the amount of a photochemical reaction of photoresist at an edge of a pattern image formed on a photoresist film.
Accordingly, although a line width of a pattern is primarily determined by the line width of a photo-exposure mask and a geometric optical configuration of a photo-exposure apparatus, a line width of a photoresist pattern may be also adjusted by controlling the photo-exposure time within a small range.
When controlling a photo-exposure time, it is necessary to first evaluate the size and quality of a photoresist pattern obtained from a previous photo-exposure time. Then, a photo-exposure time can be re-established by a kind of processing feedback according to this evaluation. In other words, an evaluation of a post-exposure step is fed back to a pre-exposure step, so that the pre-exposure step processing condition can be adjusted.
An example of the above technology is disclosed in U.S. Pat. No. 5,965,309. In this patent, a size and a shape of a resulting pattern obtained from a conventional patterning process using a photolithography and an etching are first evaluated. The evaluated result is then progressed, and a processing condition is re-established by means of a predetermined method to influence the patterning. In particular, a method is disclosed that is effective on a final pattern by adjusting a focus and an exposure rate in a photo-exposure process, in addition to the method of adjusting a condition in an etching process.
Although the above patent deals widely with techniques for conditioning photo-exposure and etching steps by adjusting patterning conditions through feedback, it does not clearly consider that a photo-exposure rate would be influenced by adjusting a photo-exposure time.
Meanwhile, a photoresist pattern obtained as a result of a photo-exposure work may be evaluated by an after-development inspection (ADI). Of course, the photoresist pattern is affected not only by various processing conditions directly related to a photo-exposure but also by a result of a pre-exposure step.
For example, if a film stacked before a photo-exposure process is made of a material having a characteristic of reflecting light well or preventing reflection, a photoresist pattern on the film is influenced by the preformed film. Certain parts of a photoresist pattern formed by a photo-exposure may be influenced by the topological pattern of a substrate surface, e.g., an uneven step coverage, formed before a photo-exposure process, or by a relative pattern position obtained after a photo-exposure process.
However, a current system for adjusting photo-exposure time cannot systematically apply a status of a result pattern or a pre-exposure step into the photo-exposure process. In addition, it has been problematic that a photoresist pattern position and a line width obtained after a photo-exposure process are variable based on the state of the power applied to a substrate.
Furthermore, in almost any manufacturing system it is necessary to periodically carry out data collection and evaluation in order use parameters obtained by a process evaluation result for the modification of a processing condition. However, it is not easy to maintain suitable processing condition in many cases while the data collection and evaluation are being carried out.
An object of the invention is to resolve the above problems. In other words, it is an object of the present invention to provide a system for adjusting a photo-exposure time by using a result of a photo-exposure process.
Another object is to provide a system for adjusting a photo-exposure time capable of enhancing a uniformity of a photoresist pattern by reflecting a feedback of factors to be compensated obtained from a post-exposure evaluation of the photo-exposure result and a feed forward of factors to be cured, obtained before a photo-exposure process.
In order to obtain the above objects, a system for adjusting a photo-exposure time in a semiconductor manufacturing apparatus, the system comprises a photo-exposure unit for adjusting a photo-exposure time of a photo-exposure step performed on a semiconductor device in the semiconductor manufacturing apparatus, in accordance with one or more adjustment signals; a pre-exposure step influence prediction unit for obtaining information about a semiconductor device in the manufacturing apparatus during a pre-exposure processing, prior to the device being subjected to the photo-exposure step, the information including a value of a factor that will influence a line width of a line formed on the semiconductor device in the photo-exposure step, and providing that information as feed forward data; an inspection unit for generating an inspection value by measuring an aspect of the semiconductor device after it has been subjected to the photo-exposure step, and providing the inspection value as feed back data; and a central processing unit for receiving the feed forward data and the feed back data, and generating the one or more adjustment signals based on the feed forward data and the feed back data.
The feed forward data is preferably obtained by quantifying the obtained information. One or more adjustment signals are preferably transmitted to the photo-exposure unit by the central processing unit in a real time.
The one or more adjustment signals are preferably generated through the use of a calculation formula, and the calculation formula preferably weights the feed forward and feed back data.
The central processing unit preferably comprises a database containing information obtained from the photo-exposure unit, the pre-exposure step influence prediction unit, and the inspection unit.
The feed forward data preferably pertains to the thickness of a film formed in processing of the pre-exposure step. The film is preferably a reflection barrier layer formed in the pre-exposure step.
The photo-exposure unit can be made to adjust a photo-exposure time based on the adjustment signals received from the central processing unit.
The pre-exposure step influence prediction unit obtains pre-exposure step processing information for a semiconductor substrate to be processed in the photo-exposure unit. Based on this information, the pre-exposure step influence prediction unit extracts the values of parameters to affect the width of a line formed in the photo-exposure unit. Furthermore, if the extracted values are difficult to be processed, the values may be quantified by a predetermined logical method. The pre-exposure step influence prediction unit stores the extracted or quantified values as feed forward data to be provided to the central processing unit.
The inspection unit checks and stores a pre-exposure step result from the photo-exposure unit. In other words, it checks a line width value for a semiconductor substrate formed in the photo-exposure unit. Instead of the pre-exposure step result value, the inspection unit may store a differential value obtained by comparing the pre-exposure step result value with a target value formed for a pre-exposure step processing. The stored values are then used as feed back data. In case a value to be compared is stored as a feed back data, a target value for a pre-exposure step should be input to the inspection unit.
The central processing unit receives data from the pre-exposure step influence prediction unit and the inspection unit. These data are applied to a predetermined programmed calculation method and are used to generate the adjustment signals. In many cases, the adjustment signals include a differential value to be corrected considering a pre-step photo-exposure time in the photo-exposure unit. Alternatively, an adjustment signal could be an optimal photo-exposure time itself.
The adjustment signal is transferred to the photo-exposure unit as intact or converted signals adaptable to the photo-exposure unit. It is desirable to transmit the signals in a real time before a semiconductor substrate is processed, to prevent some substrates from being exposed during an inappropriate photo-exposure time.
It is preferable to apply a predetermined calculation method to the central processing unit in the present invention considering a processing status. For instance, the data to be calculated in the predetermined method is stored in the inspection unit or the pre-step influence prediction unit. Among the stored data, the most recent data result may have a weighted value. In this case, the weighted value may be inputted together with the data to be calculated.
The processing steps in this invention are performed on substrate lots because the substrates in the same lot are treated by the same conditions. The three most recent lots of the processed substrates in the photo-exposure unit may be inspected so as to obtain a pre-step result. A photo-exposure time value for correction by a predetermined calculation method corresponds to a differential value for line width obtained from analyzing differential values for line widths from the previous three lots. Furthermore, a time value for correction corresponding to feed forward data may be also considered for a calculation of the time value for correction.
The photo-exposure result of multiple pre-exposure steps, i.e., accumulated data of line width values after development may be used for evaluating the influence of pre-exposure steps. For example, line width values are arranged in the ADI step for each prior processed lot. In the pre-exposure steps of each prior process, factors influencing a photo-exposure process are determined and the values are quantified.
The relation between line width values and quantified factor values may be arranged by a graph or a function. Instead of the line width values, the differential value from a line width value and a target value of the line width may be used for obtaining the relationship. When a graph or a function related to a line width from the factor values is obtained, the relationship is reflected in the predetermined calculation method.
In this invention, a reflectivity is determined by the thickness and quality of substrate surface formed in the most recent pre-exposure step process. The reflectivity may be illustrated as a factor value capable to be quantified or feed forward data.